Controlled degenerative feedback circuits



Feb. 1, 1944.

B. W. VAN INGEN $CHENAU CONTROLLED DEGENERATIVE FEEDBACK CIRCUITS Filed Dec. 13, 1938 3 Sheets-Sheet l 0 m 0% TN R mm W E T MN m 1m H w Kw mm R 1 m% M m 4 L? B 2 .Y B Piv y T F M i=7 5 D 5 w 4 m m M H m M 4 1 z z c M v T R 3 A q f H f C. L w w z 2 A w? W II M A l 3 k E II J p ATTORNEY.

Feb. 1, 1944- B. WQVAN INGEN SCHENAU ,340,

CONTROLLED DEGENERATIVE FEEDBACK CIRCUITS Filed Dec. 15. 1938 s Shets-Sheet 2 INC'ANDESCENT LAMP INVEN TOR. BEPNAADU? VAN INGENSCIIENAZ/ ATTORNEY.

Feb; .1, 1944.

B. w. VAN INGEN SCHENAU CONTROLLED DEGENERATIVE FEEDBACK CIRCUITS Filed Dec. 15, 1938 3 Sheets-Sheet 3 1 9.6. T i' K "EN 0 E A146.

T ll c. 1 2 5 [K] i,

AMC!

A TTORNEY.

Patented Feb. 1, 1944 CONTROLLED DEGENERATIVE FEEDBACK CIRCUITS Bernardus W. van Ingen Schenau,

Eindhoven,

Netherlands, assignor, by mesne assignments,

to Radio Corporation of America,

New York,

N. Y., a corporation of Delaware Application December 1a, 1938, Serial No. 245,357 In Germany January 28, 1938 19 Claims.

The present invention relates to radio receiving apparatus provided with degenerative backcoupling in order to reduce non-linear distortion. As is Well-known, degenerative back-coupling reduces the amplification, and, therefore, the sensitiveness of the receiver. According to the invention, in order to be able to receive weak signals with such a receiving apparatus, the degenerative back-coupling is made dependent on the amplitude of the received signal in such manner that with small amplitudes the degenerative back-coupling has a slight value and increases with an increasing amplitude. In the degenerative back-coupling circuit should preferably be included an impedance whose value is regulated by a control voltage which depends on the amplitude of the received signal.

The invention will be more clearly understood by referring to the accompanying drawings wherein Figs. 1 to 7 inclusive show respectively different modifications of a radio receiver according to the invention, and in which similar components are denotedby the same numerals.

The radio receiving apparatus shown in Fig. 1 comprises a high-frequency amplifier I, a mixing or first detector stage 2 provided with a local oscillator 3, an intermediate-frequency amplifier 4, a second detector 5, and a low-frequency amplifier comprising amplifying tubes 6 and 1. A

loudspeaker 9 is connected, through a transformer 8', to the output circuit of the low-frequency amplifier.. The cathode lead of the tube 6 comprises the internal resistance of a tube II which is stepped-down by means of a transformer ID. The output voltage of the transformer 8 is supplied, through a potentiometer consisting of resistances I2 and I3, to the steppeddown internal resistance in such a phase that degenerative back-coupling to the input circuit of the tube 6 is obtained.

The internal resistance of the tube II is controlled in dependence on the amplitude of the received signal by means of a control rectifier M to which the output voltage of the intermediate frequency amplifier 4 is supplied. The control voltage which is supplied by the control rectifier, and which is dependent on the amplitude of the received signal, is utilized, in addition, for the control of the amplification of one or more tubes of the highand intermediate-frequency amplifiers l and 4.

In the reception of weak signals the control voltage has a low value, and, in accordance therewlth,,.thelgrid'of the tube has only a slight negative potential. The internal resistance of the tube II is small in this case, so that the transformed internal resistance, which is connected in parallel to the resistance l2, also has a small value, and, therefore, a small proportion of the output voltage of the transformer 8 is supplied in anti-phase to the input circuit of the tube 6. The low-frequency amplifier possesses in this case a high sensitiveness, which is desirable in the reception of weak stations. When the amplitude of the received signal increases, the control voltage assumes a higher value so that the negative potential at the grid of the tube II, and therefore the internal resistance of this tube, increases. That proportion of the output voltage of the transformer 8 which is supplied in anti-phase to the input circuit of the tube 6 consequently increases with an increasing signal strength. The degenerative back-coupling' and therefore the quality of the reproduction increase in this case whereas the sensitiveness decreases.

In the circuit arrangement shown in Fig. 2 the degenerative back-coupling dependent on the signal strength is obtained by means of a tube l5 which is connected between the grid and the anode of the low-frequency amplifying tube 1. The internal resistance, which determines the value of the degenerative back-coupling, is controlled again in dependence on the control voltage provided by the control rectifier l4.

Fig. 3 represents the case in which the resistance l3 included in the degenerative back-coupling circuit depends on temperature. The temperature of this resistance is controlled in dependence on the intensity of the received signal, by means of a heating element l6 which is included in the anode circuit of an intermediatefrequency amplifying tube IT. The amplification of this tube is controlled in known manner by the control voltage of the control rectifier M. The anode current variations developed by tube I 7 act on the temperature of the heating element [6, and, therefore, on the value of the resistance l3.

In the circuit arrangement according to Fig. 4

a resistance dependent on temperature, e. g. an

incandescent lamp I8, is connected into the anode circuit of the intermediate frequency amplifier II; the amplification of the latter is controlled in dependence on the control voltage of the control rectifier M; The resistance of the incanclescent lamp [8, which has been transformed by a transformer I9, is located, in parallel to a resistance 20, in the cathode lead of the low frequencyamplifying' tube 1. Thevariation in the anode current of the tube H, which is produced due to a variation in the signal strength, causes in its turn a variation in the value of the resistance l8 and thus controls the degenerative back-coupling of the tube 1.

The circuit arrangement shown in Fig. 5 is substantiallysimilar to that according to Fig. 4, with the exception that the resistance [8, which is dependent on temperature, is connected, in series with the secondary winding of a transformer l9, into the anode circuit of the tube l1.

Besides, an impedance dependent on frequency,

viz. a condenser 2|, is connected in parallel to the said winding so that degenerative back-coupling dependent on frequency is obtained. That is to say, such a coupling is secured that with small amplitudes of the received signal, and consequently with slight degenerative back-coupling, the band of frequencies transmitted by the lowfrequency amplifier becomes narrower. This is desirable in the reception of weak stations for the purpose of obtaining a favorable ratio between signal and interference.

With the system shown in Fig. 6 the variable degenerative back-coupling is obtained by means of a bridge-connection which is connected into the cathode lead of the low-frequency amplifying tube 6, and which is constitutedby two resistances 22 and 23 which are dependent on temperature and on two invariable resistances 24 and 25. The resistances 24 and 25 are so chosen that in the reception of weak signals the bridge-connection is inequilibrium, and no degenerative back-coupling occurs. The anode current of the tube ll, whose amplification is influenced by the control rectifier I4, flows through the resistances 22 and 23 from the cathode of the amplifying tube I1. As a result, with an increase in the signal strength the resistances 22 and 23 vary, and consequently disturb the equilibrium of the bridge-connection. Thus with increasing signal strength the degenerative back coupling increases.

. In the circuit arrangement shown in Fig. 7 two voltages are taken from the output transformer, one of these voltages being led back aiding in phase through a resistance 26 and a condenser 21 to the input circuit of the amplifying. tube 6, and consequently affords retroactive coupling. The other voltage is led back in anti-phase through a variable and temperature-dependent resistance 28 to the input circuit of the tube 6 and consequently aifords degenerative back-coupling. In the case of weak signals the retroactive coupling should preferably be equal to the degenerative back-coupling, or be only slightly smaller than this coupling. With an increasing signal strength the degenerative back-coupling increases due to the variation of the resistance 28 in dependence on the anode current of the tube ll, whose amplification is controlled by the control voltage coming from the control rectifier I l, and which anode current flows through the resistance 28.

In the above-described practical xamples use has always been made of degenerative back-coupling in the low-frequency amplifier. It is evident, however, that the invention may be applied to any degenerative back-coupling; for example to a circuit arrangement in which degenerative back-coupling through at least a part of the highor intermediate-frequency amplifier is effected by modulating a low-frequency voltage on the highor intermediate-frequency signal. Also in. these circuit-arrangements the degenerative back-coupling circuit has connected into it a resistance, for example in the form of a discharge tube, of a resistance dependent on temperature or of a bridge-connection, whose value is influenced by a control voltage.

What is claimed is:

1. In a radio receiver of the type comprising an audio modulated carrier energy transmission network, a demodulator and an audio modulation amplifier network; the improvement comprising a degenerative audio voltage feedback path connected between the output and input of said audio network, said path having operatively associated therewith a temperature-dependent feedback control impedance, and means, connected to utilize modulated carrier energy, responsive to variations in solely carrier amplitude for automatically adjusting the magnitude of said impedance.

2. In a radio receiver of the type comprising an audiomodulated carrier energy transmission network, a demodulator and an audio modulation amplifier network; the improvement comprising a degenerative audio voltage feedback path connected between the output and input of said audio network, said path having operatively associated therewith a. feedback control impedance, means responsiv to variations in solely carrier amplitude at said carrier network for automatically adjusting the magnitude of said impedance, said control impedance comprising at least one temperature dependent resistance element, and said responsive means including a device for varying the temperature of said element. 7

3. In a radio receiver of the type comprisingan audio modulated carrier energy transmission network, a demodulator and an audio modulation amplifier network; the improvement comprising a degenerative audio voltage feedback path connected between the output and input of said audio network, said path having operatively associated therewith a feedback control impedance, means responsive to variations in carrier amplitude for automatically adjusting the magnitude of said impedance, and an additional audio voltage path between the output and input of said audio network for regeneratively feeding back audio voltage- 4. In a radio receiver of the type comprising an audio modulated carrier energy transmission network, a demodulator and an audio modula-' tion amplifier network; the improvement comprising a degenerative audio voltage feedbackv path connected between the output andinput of said audio network, said path having operatively associated therewith a temperature-dc pendent feedback control impedance, means responsive tovariations in solely carrier amplitude at said carrier network for automaticallyvary ing the temperature, and consequently adjusting the magnitude, of said impedance, and. connections between said responsive means and carrier. transmisslon network for regulating the tra'nsmission efficiency through-the latter. j.

5. In an audio voltage transmission system the typeincluding at least one audioamplifier tube having input and output circuits, the method which includes impressing audio voltage upon the input circuit, feeedingbackaudio voltage.

from the output to the input circuit in degenerative phase, impeding the feedback of saidvoltage, automatically adjusting the impedance to said feedback in responseto variations of volt-. age amplitude at said, input circuit, and additionally feeding back audio voltage from the output circuit to the input circuit in regenerative phase without impedance.

6. In a modulated carrier energy system of the type comprising at least one carrier energy transmission tube, a demodulator and at least one modulation voltage transmission tube, a degenerative modulation voltage feedback means operatively associated with the output and input of said modulation transmission tube, a feedback control element operatively associated with said feedback means, means for deriving a control voltage from the carrier energy, means for varying the space current of said carrier transmission tube with said control voltage, and means responsive to the varying space current for regulating said control element.

7. In a modulated carrier energy system of the type comprising at least one carrier energy transmission tube, a demodulator and at least one modulation voltage transmission tube, a degenerative modulation voltage feedback means operatively associated with the output and input of said modulation transmission tube, a feedback control element consisting of a temperature-dependent resistor operatively associated with said feedback means, means for deriving a control voltage from the carrier energy, means for varying the space current of said carrier transmission tube with said control voltage, and means responsive to the varying space current for regulating said control element.

8. In a radio receiver of the type including a carrier amplifier tube, a demodulator and an audio amplifier tube, the method which includes impressing audio modulated carrier voltage on the carrier tube, demodulating the amplified carrier voltage, amplifying the audio voltage at the audio tube, degeneratively feeding back audio voltage from the output of the audio tube to its input, deriving a unidirectional voltage from the carrier voltage, regulating the space current flow of said carrier amplifier tube with said derived voltage, and adjusting the said feedback in response to the variation in said space current fiow.

9. In a radio receiver of the type including a carrier amplifier tube, a demodulator and an audio amplifier tube, the method which includes impressing audio modulated carrier voltage on the carrier tube, demodulating the amplified carrier voltage, amplifying the audio voltage at the audio tube, degeneratively feeding back audio voltage through a temperature-dependent element from the output of the audio tube to its input, deriving a unidirectional voltage from the carrier voltage, regulating the space current flow of said carrier amplifier tube with said derived voltage, and adjusting the said feedback by varying the magnitude of said element, in response to the variation in said space current flow.

10. In a modulated carrier wave receiving system of the type comprising a modulated carrier energy transmission network, detection means, a modulation voltage transmission network and means providing modulation voltage feedback from a point in the modulation voltage network to a preceding point thereof; the improvement which comprises means responsive to solely carrier amplitude variations of a modulated wave of a desired carrier frequency for producing a control voltage, and means responsive to said control voltage for controlling the magnitude of said feedback.

11. In a modulated carrier wave receiving sysenergy transmission network, detection means, a modulation'voltage transmission network and means providing a degenerative modulation voltage feedback from a point in the modulation voltage network to a preceding point thereof; the improvement which comprises means responsive to solely carrier amplitude variations of a modulated wave of a desired carrier frequency for producing a proportionally variable control voltage, and means responsive to said control voltage for controlling the magnitude of said feedback in the same sense as the carrier amplitude variation.

12. In a radio receiver provided with at least one signal carrier transmission tube, a detector and an audio frequency network, means providing degenerative feedback of audio voltage from a later point in the audio network to an earlier point thereof, means responsive to signal carrier amplitude variation for controlling the gain of the transmission tube, and means responsive to variation in spac current flow of the controlled tube for controlling the magnitude of said degenerative feedback.

13. In a radio receiver provided with at least one signal carrier transmission tube, a detector and an audio frequency network, means providing degenerative feedback of audio voltage from a later point in the audio network to an earlier point thereof, means, responsive to signal carrier amplitude variation, for controlling the gain of the transmission tube, and means common to the space current path of the controlled tube and said feedback means, and responsive to variation in space current flow of the controlled tube, for controlling the magnitude of said degenerative feedback.

14. In a signal carrier reception system including a carrier energy transmission network and an audio amplifier circuit, a circuit connected between two successive points of the audio circuit for feeding back audio voltage, and means connected to aid carrier network and responsive to signal carrier amplitude variation for automatically adjusting the magnitude of the feedback voltage.

15. In a signal carrier reception system includ ing a carrier energy transmission network and an audio amplifier circuit, a circuit connected between two successive points of th audio circuit for feeding back audio voltage in degenerative phase, and temperature-dependent means connected to said carrier network and responsive to signal carrier amplitud variation for automatically adjusting the magnitude of th feedback voltage.

16. In an audio-modulated carrier receiver of the type provided with an audio amplifier, means for providing degenerative audio feedback between two successive points of the amplifier, and means responsive solely to the carrier amplitude variation for automatically adjusting the magnitude of said feedback.

17. In a radio receiver provided with at least one signal carrier transmission tube, a detector and an audio frequency network, means providing degenerative feedback of audio voltag from a later point in the audio network to an earlier point thereof, means, responsive to signal carrier amplitude variation, for controlling the gain of the transmission tube, and temperature-dependent resistance mean responsive to variation in space current flow of the controlled tube for controlling the magnitude of said degenerative feedback.

rier amplifier space current, in a sense such as to increase feedback as the carrier amplitude increases. 7

19. In combination with at least two cascaded signal transmission tubes, a signal feedback path between the output and input of the second tube, and means, including an element in the space current path of said first tube, for controlling the magnitude of signal feedback in response to the 10 amplitude variation of the signal.

'BERNARDUS W, v. INGEN SCHENAU, 

